The conventional sport rackets generally include a frame with a netted portion and a handle connected to the handle. The netted portion is composed of strings which can be Nylon strings, synthetic gut strings, or nature gut strings. The Nylon strings are durable but have less flexibility and are affected by changes of temperature. The nature gut intestine strings have better flexibility but are less stronger than the Nylon strings and synthetic gut strings. The conventional sport rackets are focused on the area of sweet spot which is an area on the netted portion and the players can ideally respond the balls that hit the sweet spot.
A conventional string structure is composed of periderm wires and a metal wire of predetermined length. The periderm wires and the metal wire are wrapped together along an axial direction. There is no center core for the string. Another conventional string includes a center core with periderm wires and the metal wire is wrapped along the center core. The periderm wires and the metal wire have different physical properties such as coefficient of extension. They provide flexibility and the metal wire reinforces the structural strength of the strings. However, these two conventional strings need to be improved in flexibility, durability, aid energy return coefficient.
The present invention provides a string structure that includes a hollow center core and periderm wires wrapped about a center core.